1. Field of the Invention
The present invention relates to a steering angle sensor in a vehicle for accurately sensing the steering angle of wheels being subjected to a steering operation.
2. Description of the Related Art
As a steering angle detection apparatus used in conventional vehicles, the main one consists of a steering sensor, comprised of a type of optical encoder, built into the steering column. This detects on a relative basis the rotational angle of the steering wheel. It has a structure sandwiching in a slit disk having a large number of holes on its periphery and mounted to the steering shaft and is mounted on the steering column, forming a pair with the sensor body, a photointerrupter. When the steering shaft is turned by the driving of the driver, the slit disk repeatedly blocks and transmits light, so the photointerrupter generates an electrical pulse signal, so by counting the number of the same, the relative rotational angle of the steering shaft is detected and based on that the steering direction is calculated.
The conventional steering angle detection apparatus using a steering sensor provided in the steering column calculates the absolute steering angle of the wheels based on the relative rotational angle of the steering shaft. Right after the power is turned on etc., however, the steering angle of the wheels is unknown and further the rotation of the steering wheel is transmitted to the wheels through a steering shaft, intermediate shaft, steering pinion gear, the universal joints connecting the same, and the steering rack bar etc., so there is a chance of some degree of error occurring between the steering angle calculated from the rotational angle of the steering shaft which the steering sensor detects and the steering angle which actually appears due to elastic deformation of the parts, assembly error, looseness of the joints, gear backlash, etc. With this apparatus, it is not possible to directly sense the steering angle of the wheels, so it was difficult to raise the precision of detection.